Synthesis of photochromic sodalite by a diffusion process

ABSTRACT

A novel, simple and inexpensive method of synthesizing photochromic sodalite is provided. The method is particularized by the diffusion of NaCl and sulfur into the zeolite (Na2O.Al2O3.2SiO2).xH2O, known commercially as Molecular Sieve No. 4A. A mixture of this zeolite, NaCl and a sulfur compound is heated in the presence of forming gas and for a time sufficient to cause diffusion of NaCl and sulfur into the lattice structure of the zeolite. The photochromic sodalite produced can be used in display units and in computer memories.

United States Patent 1 Dreyfus et a1.

[ SYNTHESIS OF PHOTOCIIROMIC SODALITE BY A DIFFUSION PROCESS [73]Assignee: International Business Machines Corporation, Armonk, NY.

22 Filed: June 18, 1971 211 Appl. No.: 154,651

[52] U.S. Cl. 423/328, 252/301.4 [51] Int. Cl...... C01b 33/26, C09k1/54, C09k 1/68 [58] Field of Search 23/367; 423/328 [56] ReferencesCited UNITED STATES PATENTS 4/1959 Milton 23/113 UX 4/1959 Milton 23/113OTHER PUBLICATIONS Kirk, Journal of the Electrochemical Society," Vol.

[111 8 3,760,063 1451 Sept. 18, 1973 101, Pages 461-465 (1954).

Williams et al., Journal of the American Ceramic Society," Vol. 52,Pages 139-145 (1969).

Primary Examiner-M. Weissman AttorneyHansel L. McGee et a1.

[57] ABSTRACT A novel, simple and inexpensive method of synthesizingphotochromic sodalite is provided. The method is particularized by thediffusion of NaCl and sulfur into the zeolite (Na O'Al O -2SiOg-xH O,known commercially as Molecular Sieve No. 4A. A mixture of this zeolite,NaCl and a sulfur compound is heated in the presence of forming gas andfor a time sufficient to cause diffusion of NaCl and sulfur into thelattice structure of the zeolite. The photochromic sodalite produced canbe used in display units and in computer memories.

4 Claims, No Drawings SYNTHESIS OF PHQTOCIIROMIIC SODALITE BY ADIFFUSION PROCESS BACKGROUND OF THE INVENTION INTRODUCTION Photochromismis the property of a material to exhibit different optical absorptionbands depending upon its history of optical illumination. That is, itcan be in a colored or bleached state, depending upon its exposure tolight of different wavelengths. Photochromic sodalite is found in natureand is known as Hackmanite. It is of technological importance because ofits reversible photochromic properties. It has a zeolite structurehaving voids filled with sodium, chlorine and sulfur. Chemically, it is3(Na O'AI O5ZSiO- 2NaCl(S i.e., some of the chloride ions are replacedby sulfur ions.

PRIOR ART Role of Sulfur in the Luminescence and Coloration of SomeAluminosilicates, Russell D. Kirk, Journal of The ElectrochemicalSociety, September 1954, page 461.

Irradiation Colours and Luminescence, A Contribution to Mineral PhysicsDr. Karl Przibram, London Pergamon Press Limited (195 6).

Synthetic Photochromic Sodalite, E. F. Williams et al, Journal of TheAmerican Ceramic Society, Volume 52, No.3, page 139, March 1969.

The Structure of Some Sodium and Calcium Aluminosilicates, LinusPauling, Proceedings of The National Academy of Sciences, Volume 16, No.7, July 15, 1930.

The publication of Kirk describes an attempt to synthesize photochromicsodalite by simultaneously synthesizing zeolite and filling theinterstices thereof with NaCl and sulfur. This required the fusing of A10 SiO Na CO NaCl and sulfur in the forin of Na- SO or Na S. Thisrequired several sintering and grinding steps to obtain completereaction of the starting materials. Thus it is a very time consumingoperation.

Similarly Williams et al prepares photochromic sodalite by sinteringmixtures of the above compounds with repeated grinding and heatingsteps. In another method Williams heats a mixture of Zeolite X, amaterial somewhat different than Zeolite 4A, and NaCl and dehydrates themixture under vacuum for 24 hours, after which the material is exposedto H 8 or S0 It should be noted that Zeolite X does not contain any Naions, hence this process is retarded since a basic change in the zeolitestructure must occur before the spherical structure of Zeolite 4A isapproached. Subsequently, the product is heated in hydrogen to obtainphotochromism thereinQIn yet a third method Williams prepares anefficient photochromic material via a hydrothermal synthesis. The lattermethod is a two-step process in which the starting materialsarethoroughly mixed and subsequently heated under pressure. While thehydrothermal method of preparation provides a more efficientphotochromic product, it also requires more elaborate and expensiveequipment.

SUMMARY OF THE INVENTION The present invention relates to a simplifiedmethod of synthesizing highly efficient photochromic sodalite. Themethod of the invention entails the initial heating of a mixturecomprising from about 80 percent to about 20 percent by weightNagOAhO-ZSiOgXI-EO (Zeolite Molecular Sieve No. 4A), from about 10percent to about 40 percent by weight of NaCl, and from about 10 percentto about 40 percent by weight of Na; S0 at a temperature of about 200 C.to about 350 C in vacuo for a time sufficient to remove water ofhydration, about 3 hours. The mixture is thereafter heated at atemperature range of about 650 C to about 950 C in the presence offorming gas (90 percent N, 10 percent H Heating is continued for aperiod of from about 16 hours to about 60 hours depending upon thetemperature used. For example, the higher the temperature, the shorterwill be the reaction time. After heating the samples for the prescribedperiod, the reaction product is cooled. The product is found to be apowder material having a white (or translucent) color in the presence ofvisible light and a magenta color after exposure to 3100A ultravioletlight. It has an optical absorption band in the visible light range of5200A.

In preparing photochromic sodalite different ratios of NaClzNa sO can beused to alter the kinetics associated with photochromism. For example,increasing the amount of sulfur in the form of Na SO increases the easeof coloring. However, the ease of bleaching is decreased. Chemicalcompounds other than NaCl and sulfur can be used. When NaBr is used inplace of NaCl the optical absorption band in the visible light rangewill be shifted from 5200A to somewhat longer wavelengths, e.g., 5600A.NaCl can be substituted with NaI, LiBr or Lil, each material having itsown absorption band. On the other hand other activators may conceivablybe of use, e.g., Na MnO or NaRu0 PREFERRED EMBODIMENT OF THE INVENTIONEXAMPLE I About 60 percent by weight of Na O-Al O -2SiO x- H O togetherwith 20 percent by weight of NaCl and 20 percent by weight of Na SO aredry-mixed. The powdered material in a quartz reaction vessel is placedinto a furnace and heated for about 3 hours to remove water ofhydration. The temperature is then raised to about 850 C and heating iscontinued for about 16 hours in a forming gas atmosphere. The reactionproduct is then cooled. A chemical analysis on the white crystallineproduct gave the following results:

Al ll.4 percent 0.1, Si 10.8 percent 0.7, Na 21.1 percent 1 0.6,

CI 16.6 percent i 0.2 and S =2.20 percent i 0.02

The material was found to have an absorption band at 5200A. It hadphotochromic sensitivity of about 0.05 to 0.08 j/cm. The efficiency ofthe material was determined by timed exposures.

EXAMPLE II The method of Example I was repeated except 20 percent of Nas was used in place of the Na SO The product obtained had the sameproperties as in Example I.

What is claimed is:

l. A method of preparing photochromic sodalite from the zeolite havingthe formula (Na O-Al,O -2Si- O )-xI-I O wherein said XH O is the waterof hydration in said zeolite, said method comprising the steps of aheating a mixture of about 20 percent to percent by weight of saidzeolite, about 10 percent to about 40 percent by weight of an alkalihalide selected from the group consisting of NaCl, NaBr, LiCl and LiBr,and about 10 percent to 40 percent by weight of an activator sodium saltselected from the group consisting of M1280 Na S, Na MnO and Na- RuOwherein S, Mn and Ru are said activators, at

about 3 hours to remove said water of hydration; b thereafter heatingsaid mixture from which said water of hydration has been removed in agas comprising about 90 percent N, and 10 percent H in a temperature andfor a time sufficient to remove 5 the temperature range f about 650 C tob t Said water of hydration; 950 C for about 16 to 60 hours to causesaid NaCl b thereafter, further heating said mixture from which and theS f said so to difi into the said water of hydration has been removed ina gas tice Structure of Said zeolite; and comprising about percent N2and H2 0 thereafter cooling the reaction product obtained in at atempegrature m 'f 9 about 650 C m said step (b), said reaction productbeing said zeobout c and cfmtmumg said last'named heat: lite with saidNaCl and said S in the crystal lattice ingfor a time sufficient to causethe selected alkali of said zeolite, halide and the Selene? to infuse mmthe said reaction product containing the following conlattice structureof said zeolite; Stimems c cooling the reaction product obtained in saidstep (b), said reaction product being said zeolite with A: 4% N3: 214%106 said alkali halide and said activator in the crystal on 16.6% 10.2 s2.20% 10.02 lattice of said zeolite. 5 103% 2. A method of preparingphotochromic sodalite from the zeolite having the formula (Na O'Al,O-2Si- Sam Yeacnon Pmduct havmg an absorpnon band 5200A and aphotochromic sensitivity of about 0.05 to 0.08 j/cm. 3. A method asdefined in claim 2 wherein said activator material is Na SO 4. A methodas defined in claim 2 wherein said activator material is Na S.

C bal-[ O wherein said xH O is the water of hydration in said zeolite,said method comprising the steps of:

a heating a mixture of about 60 percent by weight of said zeolite, 20percent by weight of NaCl and 20 percent by weight of an activatormaterial selected from the group consisting of Na s and Na sO at atemperature of about 200 C to about 350 C for

2. A method of preparing photochromic sodalite from the zeolite havingthe formula (Na2O.Al2O3.2SiO2)xH2O wherein said xH2O is the water ofhydration in said zeolite, said method comprising the steps of: aheating a mixture of about 60 percent by weight of said zeolite, 20percent by weight of NaCl and 20 percent by weight of an activatormaterial selected from the group consisting of Na2S and Na2SO3 at atemperature of about 200* C to about 350* C for about 3 hours to removesaid water of hydration; b thereafter heating said mixture from whichsaid water of hydration has been removed in a gas comprising about 90percent N2 and 10 percent H2 in the temperature range of about 650* C toabout 950* C for about 16 to 60 hours to cause said NaCl and the S fromsaid Na2SO3 to diffuse into the lattice structure of said zeolite; and cthereafter cooling the reaction product obtained in said step (b), saidreaction product being said zeolite with said NaCl and said S in thecrystal lattice of said zeolite, said reaction product containing thefollowing constituents: Al 11.4% + 0.1 Na 21.1% + or - 0.6 Cl 16.6% +or - 0.2 S 2.20% + or - 0.02 Si 10.8% + 0.7 said reaction product havingan absorption band at 5200A and a photochromic sensitivity of about 0.05to 0.08 j/cm2.
 3. A method as defined in claim 2 wherein said activatormaterial is Na2SO3.
 4. A method as defined in claim 2 wherein saidactivator material is Na2S.